There are known disk drive apparatuses that use various types of media such as optical disks, magnetic optical disks, and flexible magnetic disks. Of those apparatuses, a hard disk drive (HDD) is widely used as a computer storage device and has become one of the mandatory storages for present computer systems. The HDD is used not only for computer systems, but also for moving picture recording and reproduction apparatuses, car navigation systems, and in digital cameras as removable memory. The use of the HDD is increasingly broadening because of its excellent characteristics.
The HDD includes: a magnetic disk for storing data; a head slider for reading or writing data on the magnetic disk; and an actuator for moving the head slider to a specified position over the magnetic disk. The actuator is driven by a voice coil motor. The actuator turns centering around a turning shaft to move the head slider in a radial direction over the rotating magnetic disk.
The head slider includes a slider and a head element formed on a slider surface. The head element includes: a recording element for converting an electric signal into a magnetic field according to data stored on the magnetic disk; and/or a read sensor for converting a magnetic field from the magnetic disk into an electric signal. The actuator includes: an elastic suspension; and a carriage arm for fixing the suspension. The head slider is fastened to the suspension. The head slider is supported by the actuator and floats over the rotating magnetic disk with a specified gap.
Vibration of the actuator degrades the accuracy for positioning the head slider. The actuator is vibrated by the vibration of the HDD itself or an air flow in the HDD due to the magnetic disk rotation. To solve this problem, there is proposed the technology of reducing the actuator vibration due to turbulence (e.g., see Japanese Patent Publication No. 272974/2004 (“patent document 1”).
The actuator vibrations can be categorized into such modes as horizontal oscillation (sway), twist (torsion), and vertical oscillation (bending). The horizontal direction is parallel to a recording surface (principal plane) of the magnetic disk. The vertical direction is perpendicular to the recording surface of the magnetic disk. The sway mode moves the head so as to deviate from a track on the magnetic disk and therefore greatly affects positioning control. For solving this problem, an attempt is made to increase the horizontal rigidity or smoothen an air flow around the actuator.
The torsion mode signifies that the carriage arm twists. The carriage arm turns centering around its rigidity. Since the head element is positioned out of the rigidity center, the head position horizontally deviates according to the turn. For solving this problem, similarly to the sway mode, an attempt is also made to increase the rigidity or smoothen the air flow.
The bending mode signifies that the carriage arm bends toward its thin and weak portion. In the bending mode, the head element (head slider) moves and vibrates in a longitudinal direction of the actuator, i.e., in a direction regulated between the head slider and the turning shaft. Since the vibration direction (movement direction) is approximately parallel to a track, the bending mode has a smaller effect on the head position accuracy than the above-mentioned two vibration modes.
As a TPI (Tracks Per Inch) becomes high, there is an increasing demand for reducing not only the sway and torsion modes, but also the bending mode. Since the rigidity has been proven to be high, the sway or torsion mode can be accordingly improved by taking the above-mentioned countermeasures. Recently, however, the bending mode increasingly constitutes a significant fraction of degradation of the positioning accuracy.
An angle between the head element and the track varies with a position on the recording surface. The angle is generally defined by a skew angle. The skew angle is regulated by a line connecting the head element with the turning shaft center and a track's tangential direction. Typically, the skew angle is 0 near the center of the recording surface. An absolute value of the skew angle increases toward an inside periphery and an outside periphery. At the position where the skew angle is 0, the skew angle direction (skew angle's positive or negative) reverses depending on the inside periphery side and the outside periphery side.
When the head element shakes back and forth, the skew angle generates a vibrational component in an off-track direction, i.e., in the radial direction. Corrective measures need to be taken also for the bending mode in order to achieve the presently requested high TPI. However, the HDD imposes severe constraints in the height direction (normal direction against the recording surface). It is difficult to enhance the rigidity against the bending mode by increasing the thickness of the carriage arm. Increasing the thickness of the carriage arm also increases the volume thereof and greatly affects the actuator's balance or dynamics.